Tweaking buggy hash detection

This should more appropriately detect the presence of the URL
constructor, and will silently ignore any exceptions (and assume the
hash isn't buggy)

src/js/regexper.js

@@ -87,10 +87,15 @@ export default class Regexper {
   detectBuggyHash() {
     var url;
 
-    if (typeof window.URL !== 'undefined') {
+    if (typeof window.URL === 'function') {
+      try {
         url = new URL('http://regexper.com/#%25');
         this.buggyHash = (url.hash === '#%');
       }
+      catch(e) {
+        this.buggyHash = false;
+      }
+    }
   }
 
   // Set the URL hash. This method exists to facilitate automated testing